Rotor and stator wheel construction for a turbo molecular pump

ABSTRACT

A turbo molecular pump is provided with rotor and stator wheels containing thin-walled blades each having the same thickness, with the blades extending radially outwardly from a carrier body which can be either ring or disc shaped. Each blade is shaped so that the acute angle formed between the tangential plane at any given point on its surface spaced from the axis of the wheel and the plane of the wheel decreases as the distance of the point increases from the axis of the wheel.

United States Patent 1 91 it Becker 14 1 July 24, 1973 [5 1 ROTOR AND STATOR WHEEL 2,500,071 3/1950 Hans...; 416/223 CONSTRUCTION F A TURBO 3,477,331 11/1969 Becker 416/237 MOLECULARPUMP 3,644,051 2/1972 Shapiro 416/237 [76] Inventor: Willi Beekeryweilburgerstr. 40, FOREIGN PATENTS O APPLICATIONS 6333 Braunfels, Germany 519,759 l/l92l France 416/223 281,280 12/1964 Netherlands 416/237 [22] Filed: July 12, 1971 [21] Appl. No: 161,662 Primgry Eiaminer-HeMy F. Raduazo I Attorney-Torch 8c McGeady [30] Foreign Application Priority Data July 15, 1970 Germany. P 20 35 063.4 [57] ABSTRACT v V A turbo molecular pump is provided with rotor and sta- 521 U.S. c1. 415 90, 415 199 R, 416/237 M wheels containing thin'iwalled blades e having 51 1111.01. F0ld 1/26 the Same thickness with the blades extending radially 5s Fieldol search...;.....;....; 415/90, 199; outwardly from a carrier y which can be either n 416/237, 223 or disc shaped. Each blade is shaped so that the .acute 1 angle formed between the tangential plane at any given 5 References Cited point on its surface spaced from the axis of the wheel UNITED STATES PATENTS and the plane of the wheel decreases as the distance of 1-767 786 6/1930 Engmand 416/237 the point increases from the axis of the wheel. 2,011,672 8/1935 I Barker 416/237 11 Claims, 7 Drawing Figures Patented July 24, 1973 2 Sheets-Sheet l Patented July 24, 1973 3,748,055

2 Sheets-Sheet 2 mu14 m ZAZ FIG.4' F IG.5

INVENTOR Willi Becker ATTORNE S ROTOR AND STATOR WHEEL CONSTRUCTION FOR A TURBO MOLECULAR PUMP a common shaft and to cooperate with similarly shaped stationary stator wheels for producing a pumping effect. The rotor and stator wheels have rings of blades in which the blades are positioned at an angle to the plane of the wheel so that inclined channels are formed between the blades.

Various embodiments of rotor and stator wheels are known. In one embodiment the inclined channels are formed by milling the blades in a solid disc. In such an arrangement the channels and the vanes or blades which bound the channels have substantially the same dimensions, that is only half of the area of the ring of blades is passable in the axial direction. In another embodiment the wheels are formed from thin planar sheet metal sections by punching out the blades and turning the blades out of the plane of the sheet metal section. In this arrangement the ring of blades is passable over almost its full area due to the narrow thickness of the sheet metal section. Further, in another known embodiment the ring of blades is formed of individual blades or vanes inserted into and fixed in rings.

The characteristics of a turbo molecular pump are determined by its pumping speed and pressure ratio, that is the ratio of the pressures at its inlet and outlet. Both of these characteristics depend largely on the circumferential velocity of the ring of blades and, accordingly, on the velocity of the rotors, Consequently, the circumferential velocity and the rotational speed of the pump shaft are chosen as high as possible based on the strength properties-of the rotor wheels.

For the above described types of rotor and stator wheels itis given that the stresses due to centrifugal half from the carrier body and half from the blades. Further, as compared torotor wheels where the blades are formed from thin plate metal, the pumping speedof the milled blade type is smaller. However, in the sheet metal blade type of wheels the stresses resulting from centrifugal force are considerably higher, since with identical dimensions the additional loading of the carrier body by the centrifugal forces of the blades is approximately twice that in the wheels with the milled type of blade. As a consequence with identical dimention is to provide a rotor wheel for a turbo molecular pump which embodies the same or improved strength properties of the milled blade type of rotors, and at the same time has a high pumping speed similar to that of the sheet metal blade type of wheels. Therefore, in acforce for rotors with milled blades result approximately cordance with the present invention, a turbo molecular pump is provided having rotor and stator wheels formed of a carrier body with thin-walled blades of uniform thickness, and the acute angle included between the tangential plane at any given point on the surfaces of the blades spaced from the wheel axis and the plane of the wheel decreases as the distance of the given point increases from the wheel axis. Further, in such a wheel construction the following equation is satisfied:

a/tan a d/sin a 2 1r r/z wherein a is the dimension of the blades forming the ring in the axial direction of the wheel, d is the thickness dimension of the blades, r is the distance from the axis of the wheel to the given point on the surface of the blade, 2 is the number of blades in the ring of blades, and a is the acute angle formed between the tangential plane at the given point and the plane of the wheel- By means of this rotor wheel construction, with the same dimension and at the same rotation speed, a considerable reductionis achieved in the centrifugal forces acting on the carrier body of the wheel, while the pumping speed is almost the same as that for the thin sheet metal blade type of wheels.

When the centrifugal forces for the milled blade type of rotor wheel described above are equal to 100 percent, the centrifrugal forces for the thin sheet metal blade type of wheels as described above is about 150 percent while for the rotor wheels formed in accordance with the present invention the centrifugal force amounts to only about -60 percent. With these low stresses a corresponding increase in the circumferential velocity is allowed, though it should be noted that the stresses increase by the square of the circumferential velocity. Due to the increased circumferential velocity. the pumping speed is similarly increased proportionately to the circumferential velocity, and, further, the pressure ratio increases in accordance with exponential function of the circumferential velocity. For achieving a certain pressure ratio of a turbo molecular pump it is possible to do so with a relatively lower number of pressure stages each of which consists of a rotor wheel and a stator wheel.

The various featuresof novelty which characterize the invention are pointeduout with particularity in the claims annexed to and forming a part of this disclosure.

. For a better understanding of the invention, its operatsions the wheels with sheet metal blades have a total ing advantagesand specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention. FIG 1 is a plan view of one embodiment of armor wheel or a stator wheel formed in accordance with the present invention;

V FIG. 2a is a developed portion of the ring of blades in FIG. 1 taken along the line B-B;

FIG. 2b is a developed portion of the ring of blades shown in FIG. 1 taken along a line at a distance r from the axis of the wheel; 1

FIG. 2c is a developed portion of the ring of blades in'FlG. 1 taken along the line AA;

FIG. 3 is another embodiment of the rotor wheel in accordance with the present invention with the upper part of the view looking downwardly at the top of the wheel and the lower part showing the wheel in section;

FIG. 4 is a partial axially extending view of a turbo molecular pump embodying rotor wheels formed in accordance with the present invention, which wheels volved. As indicated in FIGS. 4 and 5, the carrier body of the stator wheels has the same dimension in the axial direction as the blades forming the ring of blades about 7 the carrier body. The rotor wheels constructed in acwith a plurality of blades 2 extending generally radially outwardly from the carrier body. As indicated in FIG. 2b, the blades have a thickness dimension d and the ring of blades has an axial dimension a. In FIG. 1 and 2b a point? is shown on one of the blades to locate it at a' distance r from the axis M of the wheel, the tangential plane T formed at this point or any given point on the blades includes an acute angle a with the plane of the wheel. The angle a is dependent on the distance r of the given point from the wheel axis M. For any given point P on the blades 2, the following equation is satisfied: I

wherein z is the number of blades in the ring of blades on the wheel.

In FIG. 3 another embodiment of a rotor wheel is shown formed in accordance with the present invention having an annularcarrier body 12 with a T-Shaped cross-section with the head of the T-Shaped crosssection located radially inwardly so that the radially inner portion of the carrier body has a greater thickness or dimension in the axial direction than the blades forming the wheel in combination with the carrier body.

, In FIG. 4a portion of the axial length of a turbo molecularpump is shown containing both the stator and rotor wheels located within an annular shaped housing 6. The stator ,wheels areformed in accordance with the arrangement shown in FIG. 1 and the rotor wheels are formed in accordance with the arrangement as shown in FIG. 3. The annular carrier bodies 12 of the rotor 'wheels are fixed on a shaft 3 extending centrally through the housing 6. The rotorwheels and the shaft 3' combine to form the rotor of the turbo molecular pump. One stator wheel is located between each pair of rotor wheels and each' stator wheel is held at its radi- In FIG. 5 another arrangement of aturbo molecular pump is illustrated containing stator wheels formedin accordance with FIG. 1 and rotor wheels having a different form of carrier body. The carrier body of the rotor wheels is a solid disc 7.'On one of the surfaces of the disc-shaped carrier body 7 which extends transversely of the axis of the pump a recess 8 is formed and on the opposite transverse surface a projection 9 is formed. The recesses 8 and projections 9 are shaped so that the projection of one carrier body fits into the recess on the adjacent carrier body so that the rotor wheels are aligned in a group. Each of the carrier bodies 7 contains a number of boi'es which are aligned with the bores in the other carrier bodies so that tension rods 10 extend through them for securing the individual rotor wheels together.

In accordance with the invention, the stator wheels are constructed in substantially the same manner as the rotor wheels, however, the carrier body 1 for the stator wheels does not have to be as strongly constructed as v in the'rotor wheels since no centrifugal forces are incordance with the invention, as shown in FIGS. 1, 3 or 5, can be assembled with stator wheels also formed in accordance with the invention, as shown in FIG. 1, or the rotor wheels may be combined with conventional stator wheels in the assembly of a turbo molecular pump.

The embodiments of the invention in which an exclusive property or priviledge is claimed are defined as follows:

1. Turbo molecular pump incuding rotor .and stator wheels, each said wheel comprising a ring of blades with the blades positioned at an angle to the'plane of said wheel, wherein the improvement comprises that at least one of said rotor and stator wheels includes a carrier body, a plurality of thin wall blades each having the same thickness and secured to and extending outwardly from said carrier body, said blade being shaped so that the acute angle formed between the tangential plane at any given point on the surface of each said blade and the plane of said wheel continuously decreases as the distance of the given point on said blade extends radi-- ally outwardly from the axis of said wheel, and the equation:

q/tan a d/sin a 2 1r r/z being satisfied for each given point on the surface of saidblade, wherein a is the'dirnension of said blade in the axial direction of said wheel, d is the thickness dimension of said blades, r is the distance from the axis of said wheel to the given point on the surface of said blade, z is the number of said blades on said wheel, and a is the acute angle formed between the tangential plane at the given point and the plane of the wheel.

2. Turbo molecular pump, asset forth in claim 1, characterized in that said carrier body has an annular shape.

3. Turbo molecular pump, as set forth in claim 2, characterized in that at least a portion of said carrier body in the axial direction of said wheel has a larger dimension than said blades in the same axial direction:

4. Turbo molecular pump, as set forth in claim 3, characterized in that said carrier body is T-shaped in radial cross section andthe head of its T-shaped sectio is located radially inwardly from the stem.

5. Turbo molecular pump, as set forth in claim 3, characterized in that said blades extend outwardly from the radially outer surface of said carrier body at a position thereon spaced axially from its axial end surfaces.

6. Turbo molecular pump, as set forth in claim 1, characterized in that carrier body has a solid discshape.

7. Turbo molecular pump, as set forth in claim 6, characterized in that at least a portion of said carrier body in the axial directionofsaid wheel has a larger dimension than said blades in the same axial direction.

8. Turbo molecular pump, as set forth in claim 7, characterized in that said blades extend radially outwardly from a radially outer surface of said carrier body at a position spaced axially from the axial end surfaces of said carrier body.

9. Turbo molecular pump, as set forth in claim 3, characterized in that an annular shaped housing extends in the axial direction of and encloses said wheels, an axially extending shaft positioned centrally within said housing, a plurality of said rotor wheels having carrier bodies which in the axial direction of said wheel have a larger dimension for at least a portion thereof than the axial dimension'of said blades and said rotor wheels mounted on said shaft, one said stator wheel positioned between each adjacent pair of said rotor wheels, and means for'securing said stator wheels in cess on one surface transverse to the axial direction and a projection shaped to fit into the recess in another said carrier body in the oppositely disposed transverse surface so that said rotor wheels can be nested together within said housing, each said disc-shaped carrier body having bores formed therethrough with the bores in said carrier bodies being disposed in axial alignment, and rods extending through said bores for securing said rotor wheels together. i

11. Turbo molecular pump, as set forth in claim 10, characterized in that one said stator wheel being positioned between each pair of said rotor wheels in said housing, and said stator wheels being secured within said housing with the radially inner surfaces thereof being in' spaced relationship from said rotor wheels.

ENTTEE STATES PATENT OFFICE IERWWCATE OF CORRECTION Patent No. 3 a 748 Dated uly 24 1973 V Inventor-(3) Willi Becker It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the-heading of the patent, insert:

[73] Assignee: Arthur Pfeiffer Vakuumtechnik GmbH,

Wetzlar, Germany- Signed and sealed this- 22 d day of January (SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

1. Turbo molecular pump incuding rotor and stator wheels, each said wheel comprising a ring of blades with the blades positioned at an angle to the plane of said wheel, wherein the improvement comprises that at least one of said rotor and stator wheels includes a carrier body, a plurality of thin wall blades each having the same thickness and secured to and extending outwardly from said carrier body, said blade being shaped so that the acute angle formed between the tangential plane at any given point on the surface of each said blade and the plane of said wheel continuously decreases as the distance of the given point on said blade extends radially outwardly from the axis of said wheel, and the equation: a/tan Alpha + d/sin Alpha 2 pi r/z being satisfied for each given point on the surface of said blade, wherein a is the dimension of said blade in the axial direction of said wheel, d is the thickness dimension of said blades, r is the distance from the axis of said wheel to the given point on the surface of said blade, z is the number of said blades on said wheel, and Alpha is the acute angle formed between the tangential plane at the given point and the plane of the wheel.
 2. Turbo molecular pump, as set forth in claim 1, characterized in that said carrier body has an annular shape.
 3. Turbo molecular pump, as set forth in claim 2, characterized in that at least a portion of said carrier body in the axial direction of said wheel has a larger dimension than said blades in the same axial direction.
 4. Turbo molecular pump, as set forth in claim 3, characterized in that said carrier body is T-shaped in radial cross section and the head of its T-shaped section is located radially inwardly from the stem.
 5. Turbo molecular pump, as set forth in claim 3, characterized in that said blades extend outwardly from the radially outer surface of said carrier body at a position thereon spaced axially from its axial end surfaces.
 6. Turbo molecular pump, as set forth in claim 1, characterized in that carrier body has a solid disc-shape.
 7. Turbo molecular pump, as set forth in claim 6, characterized in that at least a portion of said carrier body in the axial direction of said wheel has a larger dimension than said blades in the same axial direction.
 8. Turbo molecular pump, as set forth in claim 7, characterized in that said blades extend radially outwardly from a radially outer surface of said carrier body at a position spaced axially from the axial end surfaces of said carrier body.
 9. Turbo molecular pump, as set forth in claim 3, characterized in that an annular shaped housing extends in the axial direction of and encloses said wheels, an axially extending shaft positioned centrally within said housing, a plurality of said rotor wheels having carrier bodies which in the axial direction of said wheel have a larger dimension for at least a portion thereof than the axial dimension of said blades and said rotor wheels mounted on said shaft, one said stator wheel positioned between each adjacent pair of said rotor wheels, and means for securing said stator wheels in said housing spaced radially outwardly from said shaft.
 10. Turbo molecular pump, as set forth in claim 6, characterized in that an annular shaped housing extends in the axial direction of and encloses said wheels, a plurality of said rotor wheels each having solid disc-shaped carrier bodies are positioned within said housing, said disc-shaped carrier bodies each having a recess on one surface transverse to the axial direction and a projection shaped to fit into the recess in another said carrier body in the oppositely disposed transverse surface so that said rotor wheels can be nesTed together within said housing, each said disc-shaped carrier body having bores formed therethrough with the bores in said carrier bodies being disposed in axial alignment, and rods extending through said bores for securing said rotor wheels together.
 11. Turbo molecular pump, as set forth in claim 10, characterized in that one said stator wheel being positioned between each pair of said rotor wheels in said housing, and said stator wheels being secured within said housing with the radially inner surfaces thereof being in spaced relationship from said rotor wheels. 